How Wide Is A W108 Radiator And Oil Cooler Combination?

[Squiggle Dog]

At some point I will be getting a W111 sedan and putting an OM617 turbo diesel engine into it. This engine will require an oil cooler, and the W111s do not have this feature. So, I'm trying to determine what model has a radiator and oil cooler combination that will fit the W111.

The opening in the radiator core support of a W111 is about 23 1/4" wide. I tried fitting the most narrow W116 combinations (a 300SD radiator with a 280SE oil cooler) and they were at least 2" too wide.

I am thinking and hoping that the radiator core support on a W108 is the same width as a W111 because I know some came with an oil cooler and it would be great if the radiator and oil cooler combination would drop in.

[ScooterABC]

I ran into a similar problem when transplanting a W108 280S engine (1968) into my W108 250S (1967). The 250S has an oil cooler that is NOT part of the radiator. It's a heat exchanger that resides near the left (driver side) engine mount arm. Since the 250S came without an engine, I was in search for an oil cooler that would work with the 250S radiator. What I eventually did was find a junked 250S and get all of the plumbing for the oil cooler and add it to the 280S. Worked fine.

I _think_ I couldn't use the radiator from the 280S because it was 2 inches to wide to fit in the opening of the 250S, so maybe we are talking about exactly the same problem. You might want to look in EPC and see how the oil was cooled on a 250S. Might provide some ideas if nothing else.

[Tomguy]

Also of note, is that although the oil cooler mounts to the radiator, it's a separate unit (or at least was on my 4.5). On the 3.5/4.5 (and presumably 6.3) it's on the RIGHT (passenger) side of the engine bay.

What I would suggest to you, would be to use an aftermarket oil cooler if you can't find the proper-sized MB parts that will work with a W111 in this application. The upside to this is if you have a U-Pull-It yard nearby, you can go in there and see tons of different sizes and applications of oil coolers (including trans coolers that you can use for this application as well), and find one that can mount in front of the radiator or in another location perhaps in the engine bay or elsewhere.

You can also use universal kits that are surprisingly cheap:
https://www.ebay.com/itm/30-Row-10AN-Universal-Engine-Transmission-Oil-Cooler-7-Fixed-Cooling-Fan-Kit/262780853733
https://www.ebay.com/itm/30-Row-10AN-Universal-Engine-Transmission-Oil-Cooler-7-Fixed-Cooling-Fan-Kit/273021712175

[Squiggle Dog]

I used to have one of those heat exchangers that I removed from a 250SE at a wrecking yard.


But, they are super expensive on eBay. Wow. I didn't get nearly that much for mine when I sold it. I just wonder, though, if it would be adequate for the OM617 turbo diesel engine, as they typically came with enormous oil coolers that were twice the size of even the ones the gasoline models had.

I'd feel okay running a smaller oil cooler, but not so sure about the heat exchanger on the side of the engine (just because I don't know if it would be efficient enough for this particular engine), though I do like that it uses hard lines instead of hoses. I'm probably going to have to relocate the oil tower anyway, as it would hit the brake booster (photo is of a 1967 W111 230S I had that was too rusty to continue).


The car didn't have power steering, so I eliminated the power steering pump bracket that hit the battery tray


I considered getting a non-turbo OM617 engine block from a W115 300D because it has the oil filter mounted down toward the bottom of the engine, and then putting the turbo pistons and head onto it so it would become an OM617 turbo engine with the oil filter down on the bottom so it wouldn't hit the brake booster. But, I don't know if those engines had an oil cooler, or if there is a canister available from a gas engine that has fittings to attach an oil cooler or heat exchanger.

I think the radiator openings on all the W108s are the same, but cars which had oil coolers attached to the radiator had narrower radiators so they would still fit in the space. If the W108 radiator opening is the same width as the W111 sedan, then theoretically I should be able to find a radiator and oil cooler from a W108 and use them.

If the detachable oil coolers on the W108 are on the right (passenger) side, that wouldn't be useful for me as I need it to be on the left (driver) side, but I think all the ones I've seen so far are on the left side.

I'm hoping for the car to appear 100% stock, even though the engine obviously wasn't available when the car was made. I'm going to be installing a parallel-flow condenser in front of the radiator (maybe even two stacked on each other as a puny 14X18" is about the largest that will fit), so that won't leave any room in front of the radiator for an oil cooler.

I could probably put an oil cooler off to the side behind the bumper or something, but this gets convoluted once I stray off of way the factory would have done it.

Worse case scenario, I could just have a radiator and oil cooler custom made, or get a W108 radiator and oil cooler and take the radiator apart and shorten the tanks and cut off one side of the core to make it narrow enough to fit--maybe even have a new thicker core installed. But, I don't think I want a custom-looking radiator and oil cooler in there, and would like to find something that's a drop-in solution.

Oh, and one thing that got me to thinking that a W108 radiator and oil cooler might fit, is that the 230S pictured above had a 108 part number radiator in it which fit perfectly, and being that the cars are from similar eras, it may be possible.

[ScooterABC]

My recollection is that the radiator opening size on the 250S was indeed smaller than the radiator opening size on the 280S. I could be wrong, but I think that's why I had to go down the path of using the oil cooler / heat exchanger from the 250S that I salvaged with the 280S engine in the 250S car.

The heat exchanger does have water flowing through it, so it might be the same amount of cooling as one that is on the side of the radiator. I don't know.

[Tomguy]

I'd suspect crankcase contamination from leaking coolant would be why the heat exchanger was discontinued, it's almost surely better in every way cooling and heating wise (As an engine that gets up to temp faster is more efficient and better lubricated, sometimes just as important as cooling a hot one).

[Squiggle Dog]

It's possible the W108 was revised to a second generation at some point and from a certain manufacture date they started making the radiator openings wider to accommodate an oil cooler.

The problem with the heat exchanger is that air cools oil better than hot coolant, so it's probably the most likely reason they were superseded by oil coolers.

The OM617 engine gets up to operating temperature just fine on its own. Because it's turbocharged and worked harder than a naturally aspirated engine, the pistons can get really hot, so there are actually piston oil squirters that help cool and lubricate them. The turbocharger also gets very hot and oil is directed onto the turbo bearings.

All this oil needs to be cooled down quite a bit by the oil cooler to make a turbocharged engine feasible and long-lasting. I am a bit skeptical about a heat exchanger being as effective as it needs to be on this particular engine.

[ScooterABC]

If air cools off oil faster than hot coolant then I think you are correct that a heat exchanger wouldn't be the best way to go.

[Squiggle Dog]

It appears the oil canister on a W115 300D engine has connections for an oil cooler, so that's good.


Though I'm not sure if a Sanden compressor would fit down in that area where it usually goes on a turbocharged engine (where the power steering pump is on the engine above). But, I think that I could use a York compressor bracket as the naturally aspirated engines use and then put a York-to-Sanden adapter on it to fit a Sanden in its place. That would actually be more ideal because the air conditioning holes in the firewall are on that side.

[ScooterABC]

Would it be cost-effective to have a radiator and oil cooler custom built to fit your space?

[Squiggle Dog]

Originally Posted by ScooterABC

Would it be cost-effective to have a radiator and oil cooler custom built to fit your space?

Maybe. It seems like they are pretty cheap to have built to spec these days if it comes to that. I'd really prefer ones that look original if possible. Then again, original oil coolers seem to cost more (even dented up used ones on eBay) than what it might cost to have a custom radiator and oil cooler made. It's also sad that radiator shops won't rebuild or weld the old aluminum oil coolers.

But, I could see sectioning the upper and lower tanks on a W108/W110/W111 radiator so a W108 oil cooler would fit next to it and then just using a thicker core to compensate for the narrowing of the radiator. Hopefully the W108 oil cooler would be the flat-side type that screws into the radiator core support.

Using a stock W108 oil cooler (that will screw into the radiator core support) and then narrowing and recoring a W108/W110/W111 radiator is probably what I'll do unless there is a W108 radiator and oil cooler that will drop right in, or I can get a custom built radiator and oil cooler that's economical and doesn't look too out of place.

[Squiggle Dog]

I just had a realization that the radiator in my W110 230 station wagon is likely wider than the radiator in any other W110 because it's moved forward in the radiator core support and takes up the whole space, instead of like other W110s where the radiator opening tapers in to the radiator.


I remember that when I had the rusty W111 230S, I tried fitting a radiator from a W110 200D and a 4" wide oil cooler from a W114, and it fit in the space. So now I am thinking that a W110 radiator and an oil cooler from a W108 would probably fit perfectly if I attach a bracket to the side of the radiator for an oil cooler to fit.

My 230 station wagon has a coolant expansion tank and I think I would like to continue to use it, so I might get a radiator from a W110 190/200(D) and maybe cut off the radiator cap mounting area from the top tank and have it patched, thus deleting the radiator cap and having a tube brazed on so a hose could be run to the expansion tank, OR maybe just leaving it as-is with a radiator cap on both the radiator and the expansion tank. Or maybe an expansion tank isn't needed? I dunno.

I'd want to have the W110 radiator recored with as thick and efficient of a core as possible to make up for the area lost by the oil cooler. The local wrecking yard has a W110 in it and the radiator looked good. Maybe I could get it, if nothing else, to use for dimensions, and then sell it if I decide to not keep it.


One way or another, this turbo diesel fintail station wagon project is going to come together. I'm still looking for a non-rusty W111 sedan donor body, preferably with a sunroof. One day this rusty-beyond-saving wagon will be my daily driver.

[ScooterABC]

Can an automatic transmission oil cooler be used as an oil cooler if you have a car with manual transmission? My W112 has a trans cooler under the radiator. But it doesn't have any fins or anything and I don't know how big the capacity is...

[Squiggle Dog]

Originally Posted by ScooterABC

Can an automatic transmission oil cooler be used as an oil cooler if you have a car with manual transmission? My W112 has a trans cooler under the radiator. But it doesn't have any fins or anything and I don't know how big the capacity is...

If you mean the section in the lower tank of the radiator as on most Mercedes radiators, it could be used for oil cooling, but it wouldn't be adequate because the inlet and outlets are too small to have good flow, and routing the hoses to it would be awkward. It would also be a cooled by hot coolant.

If you mean a separate transmission cooler that mounts under the car, it may work, but still probably wouldn't work as well as having one mounted to the side of the radiator and might be awkward.

I'll probably either end up using a W110 190/200(D) radiator with a W108 oil cooler on the side, have a thicker and more efficient core put in the W110 radiator, and then get a W108 radiator and swap out the oil cooler mounting bracket onto the W110 radiator. Then maybe have the filler neck of the radiator turned 180 degrees so the overflow tube can attach to the hose going to the expansion tank.

Maybe have a radiator cap on both the radiator and the expansion tank, or cut off part of a tank off another radiator and braze it to make a filler delete.

Or, I'll have something custom made, but would rather have it look like the car was made like this. I want to make a car that Mercedes didn't, but should have, made, in the way they would have made it. Even though it will be very custom, I want it to appear stock.

[Rook]

Here are the measurements I got off my 1969 280S today. The oil cooler is on the lefthand driver’s side.

Width of opening overall: about 27 1/2 inches
Width radiator alone: about 23 inches
Width of oil cooler alone: about 3 1/4 inches

The inch or so discrepancy between the combined width of the two components and the width of the opening is the thick rubber on the sides (visible in the first photo below).

Height of radiator is about 19-20 inches

The radiator (including cap) is about 2 inches higher than the oil cooler. The oil cooler is tucked in where the hood slopes down from the tall grille.

Hope this helps; it looks like a very interesting project!